1. Field of the Invention
The present invention relates to a crank shaft, in particular, capable of improving the conversion efficiency between rotational movement and linear movement by using an elastic member.
2. Description of the Related Art
In general, a crank shaft is widely used for an engine of a vehicle, a compressor and the like functioning as a member for converting rotational movement into reciprocating movement.
FIG. 1 illustrates the structure of a conventional crank shaft.
Referring to FIG. 1, the conventional crank shaft comprises: a rotation shaft 30 connected to a rotation member 10 for rotating the rotation shaft 30; and a crank arm 40 which is connected at the center to the rotation shaft 30 and at one side to a connecting rod via a crank pin 50. At one end of the connecting rod 60, is provided a reciprocation member 20 moving according to the reciprocating movement of the connecting rod.
To be more specific, the rotation member 10 rotates the rotation shaft 30, in which the rotation of the rotation shaft 30 is directly transferred to the crank arm 40 rotating the same. In this case, the crank pin 50 is biased from the center of gyration of the crank arm 40 for a predetermine distance to rotate in a circle having a predetermined radius due to the rotation of the rotation shaft 30.
The connecting rod 60 connected to the crank pin 50 converts the circular movement of the crank pin 50 into vertical reciprocating movement. The vertical movement of the connecting rod 60 vertically moves the reciprocation member 20 connected thereto.
Alternatively, the operation can be carried out reversely from the above. In other words, the reciprocation member 20 is operated to vertically reciprocate the connecting rod 60 connected thereto. The connecting rod 60 circularly moves the crank arm 40 accordingly rotating the rotation shaft 30 so that the rotation member 10 connected to the rotation shaft 30 performs a certain operation.
The crank shaft is the member capable of converting the rotational movement into the reciprocating movement. Such a crank shaft is generally used in the modern society. For example, a vehicular engine rotates the rotation member due to the reciprocating movement of the reciprocation member. On the contrary, the rotation of the rotation member makes the reciprocation member reciprocate in a compressor used for a refrigerator or an air conditioner.
FIG. 2 illustrates the structure of a reciprocating compressor adopting a conventional crank shaft.
Referring to FIG. 2, the conventional reciprocating compressor comprises a closed vessel 1 defining a housing of the compressor, a frame 2 installed inside the closed vessel 1, a drive motor M constituted of a stator 3 and a rotor 4 installed under the frame 2, a crank shaft 30 coupled to the inside diameter of the rotor 4 of the drive motor M and having an eccentric section at one end, a connecting rod 60 connected to both of the eccentric section of the crank shaft 30 and the lower end of a piston 22 for converting the turning effect of the crank shaft 30 into linear reciprocating movement, a cylinder 21 coupled to an upper portion of the frame 2 and the piston 22, in which the piston 22 is connected to the connecting rod 60 coupled to the eccentric section of the crank shaft 30 to linearly reciprocate within the cylinder 21.
Here, the one side of the crank shaft 30 is fixedly connected to the connecting rod 60 through a crank pin.
The cylinder 21 is provided with suction and discharge valves for sucking and discharging a coolant gas into/from the cylinder 21, in which the valves are surrounded by a muffler 8.
Describing the operation of the reciprocating compressor configured as above, operation of the drive motor M primarily rotates the crank shaft 5, and accordingly the connecting rod 60 performs circular movement also. Since the connecting rod 60 is connected to the piston 22 placed inside the cylinder 21, the circular movement of the connecting rod 60 allows the piston 22 to perform linear reciprocating movement. The reciprocating movement of the piston 22 is used to suck, compress and discharge fluid.
However, since the conventional crank shaft has the crank pin fixed to the connecting rod, the loss according to overpressure is generated in the compression process as the rotation force of the crank shaft is transferred to the connecting rod as it is. Also, in case of the sucking process, the maximum efficiency of the conventional reciprocating compressor is decreased as the piston connected with the crank shaft through the connecting rod sucks the coolant less than the maximum sucking volume.